Hydraulic pumps or motors



June 16, 1964 c5. BECK ETAL 3,137,243

HYDRAULIC PUMPS 0R MoToRs Filed June 5, 1959 5 Sheets-Sheet 1 GEORGEBECK ERIC HIDE BOWERS PETEI? HENRY BROWN OSWALD THOMA i Y Mm @www +4ATTORNEYS June 16, 1964 G. BECK ETAL 3,137,243

HYDRAULIC PUMPS OR MOTORS Filed June 5, 1959 5 Sheets-Sheet 2 4/ 59 2/39 6/ J /V/ J 67( y J 68 1 e nu.

INVENTOES GEORGE BECK ERIC HIDEIZ, BOWERS' PETER HENRY BROWN BY OSWAL-DTHOM A W w+ A'rToQNEYS June 16, 1964 G. BECK ETAL HYDRAULIC PUMPS 0RMoToRs 3 Sheets-Sheet 3 Filed June 5. 1959 INVENTOES GEORG E BECK.

ERIC HIDEIZ BOWERS PETER HENRY BROWN oswALD THOMA .,.wa/MAM BY WATTORNEYS United States Patent 3,137,243 HYDRAULIC PUMPS OR MOTORSGeorge Beck, Tewkesbury, Eric Hider Bowers, Cheltenham, Peter HenryBrown, Prestbury, and Gswald Thoma, Cheltenham, England, assignors toDowty HydraulicUnits Limited, Tewkesbury, England, a British company,and Oswald Thoma, Cheltenham, England Filed .lune S, 1959, Ser. No.818,291 l Claim. (Cl. S-162) This invention relates to hydraulic pumpsor motors of the class comprising a rotary cylinder block havingcylinders parallel or substantially parallel to the block rotation axis,a rotary thrust plate and drive shaft secured together and mounted forrotation about an axis intersecting the rotation axis of the cylinderblock, pistons inthe cylinders, a connecting rod articulatingly securedbetween each piston and the thrust plate, a universal joint arrangementto interconnect the thrust plate and cylinder block to ensure that theyrotate similarly, and valve means co-operating with the cylinder blockot connect the cylinders to supply and return ports during rotation insynchronism with reciprocation of the pistons within their cylinders. Inthis class of pump or motor the displacement may be fixed or variable byarranging that the cylinder block is either mounted so that itsrotationV axis intersects the thrust plate axis at a xed angle or,alternatively, is hingedly mounted so that its rotation axis isangularly adjustable relatively to the thrust plate axis. In order to beable ,to obtain a large liquid flow rate in such a pump or motor it isdesirable that it should be capable of high speed operation with a largeangle between the rotation axes of the cylinder block and thrust plate.This requires that the universal joint should have exact constantvelocity characteristics at any angle to avoid unduly large cyclicaccelerating and decelerating forces being transmitted through theuniversal joint. It is known to provide two Hooke type universal jointsin series between the thrust plate andcylinder block so arranged thattheir non-constant velocity characteristics oppose one another to give asubstantially constant velocity relation. However, in such a case one ofthe joints is necessarily located partly within the cylinder block andit follows that its size and consequently the torque that it cantransmit without substantial wear over a longL period is limited by thespace available between the cylinders. Further, where the displacementis variable by varying the angle between the two axes the Hooke jointcombination is not accurate in securing constant velocity relation overthe whole range of displacement variation. Still further, lost motionmay easily occur in the Hooke joint combination and create difculty inmaintaining exact phase relationship between the cylinder ,block and thethrust plate.

The use of a single constant velocity universal joint to interconnectthe thrust plate and the cylinder block would solve the difficultiesmentioned above, in particular it would allow high speed operation witha large angle between the rotation axes of the thrust plate and cylinderblock and, at the same time, maintain exact constant velocitycharacteristics. Further, such a joint would be located at theintersection of the two rotation axes which is at a position between theconnecting rods where the largest space is available. Such a joint isknown to the art, and in its general form is not a part of thisinvention. However, a further difficulty arises in its use in that, forsuccessful operation, the geometric centre of the universal joint mustcoincide exactly with the intersection ofthe rotation axes of the thrustplate and cylinder block. In practice, this is never possible due tomanufacturing tolerances and any attempt to use a pump or motor of the'class described having a known type of constant vep locity universaljoint as the sole interconnection between ice thrust plate and cylinderblock could only result in heavy stresses in the universal joint whichwould cause rapid wear.

The main object of the present invention is to provide a pump or motorof the class described having a constant velocity universal joint ofknown type as the interconnec* tion between thrust plate and cylinderblock together with novel compensating means for manufacturing or othertolerances that will allow the constant velocity universal joint,despite displacements impossible to eliminate, to operate substantiallyas though it were located exactly at the intersection of the tworotation axes.

In accordance wih the present invention, in a pump or motor of the classdescribed a constant velocity universal joint is provided tointerconnect the thrust plate and the cylinder block and is located sothat its geometric centre coincides substantially, or as nearly as ispracticable, with the intersection point of the two axes of rotation,the connection between this universal joint and either the thrust plateor the cylinder block being arranged to allow at least of small degreesof lateral bodily movement of the part connected to the driving shaftrelative to the part connected to the other element, and with relationto their common rotation axis. Where the constant velocity universaljoint cannot permit of longitudinal movement of the cylinder block orthrust plate along their respective axes it is desirable to include inthe connection to the thrust plate or cylinder block means to allow suchlongitudinal movement. It is, however, the relative bodily movement thatdistinguishes this invention, as distinct, from lateral ilexure. Theconstant velocity universal joint may enter a recess in the thrust platehaving a diameter extending almost to the articulating connections ofthe connecting rods whereby the torque capacity of the joint may be madeas large as possible. It is preferred that the constant velocityuniversal joint should be secured directly to the cylinder block andthat the connection oifering relative movement should be between theuniversal joint and the thrust plate. The connection affording relativemovement may be one such as is disclosed in the Brown Patent No.2,900,921, where the movement is permitted by the spring in a shaftmounted within a bore in the driving shaft, modified, however, in thatthere is a splined connection between the spring shaft and the universaljoint half to which it is connected whereby relative movement betweenthe universal joint and the thrustplate may be not only lateral, due tothe spring in the shaft, but also longitudinal relative'to the thrustplate axis, due to the splined connection, and hence in any direction,or universal-or there may be in actual fact a secondary universal jointbetween the thrust plate and its half of the primary universal jointhalf, whereby bodily relative universal movement of slight magnitude mayoccur. Preferably, and distinctive in this invention, the connectionoffering transverse angular and longitudinal relative movement is anelementary form of universal joint comprising a slot or slots andsliding member tting in the slots.

Five examples of the invention will now be described with reference tothe accompanying drawings, in which:

FIGURE l is an axial section through a pump of the kind describedembodying the flexible shaft extension which illustrates the principleof the invention, but with- Y out change over the Brown patent;

spectively still further examples, which also are entirely practical. Yn

Reference is made initially to FIGURE l to illustrate the principleunderlying the more practical forms later described. In the drawing adriving shaft 1 of the pump is provided having splines 2 to facilitatepositive connection to a driving means. This shaft extends into ahousing 3 and increases in cross-section to terminate as the thrustplate 4. The driving shaft 1 and thrust plate 4 are made from a singlepiece of metal and xedly located by r'rieans such as the roller bearings5 and 6 against radial movement and by the thrust roller bearing 7against endwise movement. The shaft V1 and thrust plate 4 include acentral bore 8 in which is located a shaft extension 9 constituting partof the connecting means referred to above which extends to one half 11of a universal joint 12. This universal joint is a type known in the artas a constant velocityuniversal joint, the function whereof `is tomaintain a constant rotational velocity of the driven element 29, withconstant velocity of the driving element 4. The joint is located in anenlargement l@ at the outer end of bore 8 which is the largest spaceavailable havingl regard to the fact that the connecting rods 41 divergefrom the cylinder block to the thrust plate, the circle containing ballends 43 being larger in diameter than the circle of the cylinders 38.The shaft extension 9 includes a portion 13 of reduced diameter to allowof small lateral spring deflections of the half 11 of the universaljoint withV relation to the driving shaft 1. The outer end of the shaft13 is formed with a splined or serrated portion 14 which is of hardenedmetal, the ends or the serrations being sharp. The portion 14 isarranged to be a drive tit in a comparatively soft metal bush 15 locatedat the end of the bore 8. A small diameter drawshatt 16 is integral withand extends from the portion 14 through a small diameter hole 17 inshaft 1, terminating adjacent the outer end of the shaft in ascrew-threaded portion 18. Arecess 19 in the outer end of shaft 1accommodates a nut 21 in screwthreaded engagement with screw 1@ suchthat rotation of the nut relatively to the draw-shaft 1t? will pull thelatter to cause the portion 14 to enter the metall bush 15 moving fromleft to right.

The above describes the shaft extension 9 as part of the connectionbetween the driving shaft 1 and the thrust plate on the one hand, andthe universal joint part 11 on the other. The invention is not limitedto such a location and association, for in other forms the halt of theuniversal joint attached to the cylinder block might equally well bearranged for connection through a similar element.

The housing 3 extends on either side of the thrust plate 4 in the formof two circular discs 22 and 23. These discs are surrounded by rollerbearings 24 and 25 which in turn fit into recesses formed in the ends ofhollow arms 26 and 27. The arms 26 and 27 extend along the side of thecylinder block and are secured to a valve plate 2S on which the cylinderblock 29 rotates. The valve plate includes two ports 31 and 32 whichconnect to passages 33 and 34 which extend through the hollow arms 27and 26 respectively. The opposite ends of the hollow arms are locatedlin bearings respectively 35 and 36 formed in the pump casing 37, thesetwo bearings being arranged to lie coaxially with the roller bearings 24and 25 and with the geometric centre of universal joint 12.

A plurality of cylinders 38 are'formed in the cylinder block 29 arrangedsymmetrically in the block with their axes parallel to the axis of blockrotation. In each cylinder a piston 39 is slidably located and from eachpiston a connecting rod 41 extends to the thrust plate. Each connectingrod is located in its respective piston by means of a ball end 42whilst, at the same time, its opposite end is located in the thrustplate by means of a ball end 43. The block 29 is rotated by means of theuniversal joint 12 and that half 44 of the universal joint whichco-operates with the half 11 is directly mounted on the end of the block29 adjacent the thrust plate. The block is retainedl iirmly seated onthe valve plate by means of a tixed shaft or stern 455 extending fromthe valve plate through a central bore 46 in the block. The end of thestem 45 is enlarged at 47 and forms a location for a sealing ring 48which seals in the bore 46. vA passage 4g extends along the shaft 45 andsupplies liquid under pressure into the bore 46 which then acts to urgethe block on to the valve plate. Pressure liquid obtains access to thehole 49 through one or the other of two one-way valves 51 or 52 locatedrespectively in the ports 32 and 31. A compression spring 53 located inthe bore 46 acts through an axial thrust bearing 54 against the enlargedend 47 of stem 45 also to urge the block against the valve late.

p The passages 33 and 34 extend through bearings 36 and to iixed pipes55 and 56 by which supply and return liquid may enter and leave thepump. The cylinder block 29, valve plate 28, and arms 26, 27 form acomplete assembly which is movable about the common axis of the bearings24, 25, 35 and 36 to vary the angular position about this axis of thethrust plate relatively to the cylinder block and so as to vary pumpdisplacement. This angular position is controlled by means of a screwadjustment (not shown but known in the art) manually adjustable fromexternally of the casing 37 and acting through a pin 57 secured to arm26.

In operation, the pump is driven at drive shaft 1 to cause both rotationof the thrust plate 4 and the cylinder block 29. Assuming that the axesof the thrust plate and cylinder block are inclined by a controllingforce applied to pin 57, the rotational movement will causereciprocation of the pistons within their cylinders. The arrangement ofthe valve plate 28 is such that cylinders having ascending pistons areconnected to one of the ports 31 or 32 and cylinders having descendingpistons are connected to the other of these ports, and liquid is pumpedfrom one ot' the passages 33 and 34 to the other passage. The directionof pumping will depend on the direction in which the cylinder block hasbeen inclined relatively to the thrust plate. For operation at highspeeds it is essential that there should be constant velocityrelationship in the universal joint between block and thrust plate. If,for example, a universal joint of the known Hooke type were used itwould be subject to cyclic alternating torques because of thenon-constant velocity relation and would rapidly wear out. The universaljoint 12 shown is of a comparatively new but known form. Briefly, thetwo halves 11 and 44 of this universal joint are each of U- shape, thelimbs interengaging one with the other through the medium of a pluralityof pads 58 semi-cylindrical in shape which are arrangedto rock'on thelimbs and slidingly engage one another. This form of universal jointgives a constant velocity drive between the two halves, whilst, atthersame time, it can allow considerable relative movement of the twohalves of the joint along their rotational axes. In the pump embodimentas described the whole pump may be completely assembled with the shaft 9and the half 11 of the universal joint displaced to the left from theposition shown in the drawing so that the serrated portion 14 is inlposition to enter, but has not entered the soft metal bush 15. Thefinal operation in the assembly of the pump isto ensure that thecylinder block is correctly alignedv vrelatively to the thrust platebefore the nut 21 is tightened to pull the portion 14 intothe bush 15,which action will iix the half 11 of the universal joint relatively tothe thrust plate 4 and thus will locate the cylinder block relatively tothe thrust plate. The two halves 11 and 44 of the universal joint comeapart leasily in the event that it is desired to take the thrust platefrom the cylinder block during servicing or repair of the pump.

The function of the shaft extension 9 and its thin part 13 is toaccommodate any slight inaccuracies in the positioning of universaljoint 12, such accommodation being by transverse bending of the portion13. Inaccuracies in commodate unavoidable lack of coincidence betweenthe center of the universal joint and the point of intersection of therelatively inclined axes of the driving and driven elements, ordisposition of these two axes so that they fail to intersect. Thisnecessity for relative movement may arise regardless of the necessityfor phase adjustment, and'may be accommodated by constructions otherthan that disclosed in the Brown patent, alternative constructions beingdisclosed herein.

A more usual` constant velocity joint may be used if` a sliding joint isprovided in shaft extension 9. Such an arrangement is shown in thesecond example illustrated in FIGURE 2. The cross-section in this ligureis at right-angles to that shown in FIGURE 1 and the cylinder block isshown with its axis inclined to the axis of the thrust plate. Wherepossible, the same reference numerals will be used to indicate partssimilar to those appearing in FIGURE 1. Thev constant velocity joint 12is of a well-known type comprising i a hollow spherical outer member 61positively secured by a support 62 to the end of the cylinder block, aninner spherical member 63, cooperating grooves'64 on the inside of theouter member 61 and the outside of the inner member `63 and a ball race65 carried by a cage '66 which locates one ball in each pair ofco-operating grooves 64. Whatever the angle between the axes of rotationof the inner member 63 and the outer member 61 the plane occupied by theball race 65 will bisect this angle and give a constant velocityrelation between thetwo parts 61 and 63.

For connection of the inner member 63 to the thrust platea splined hole67 is formed` axially in member 63 which receives the splined end 68 ofthe thin spring shaft 13 extending back into the bore 8.` The shaft 13terminates in the flange 59y which may be locked against a shoulder inthe bore 8 by means of a drawbolt 16 extending through a small hole inthe Vdrive shaft 1 and a nut 21 located at the outer end of thedriveshaft.

vDuring rotation of the drive shaft 1 and cylinder block 29 anyinaccuracies in the location of the universal joint 12p so that eitherits centre does not coincide with thev supposed point of intersection ofthe two rotation axes of the thrust plate 4 and cylinder .block 29, and/or the two axes do not actually intersect, areV accommodated by the factthat the shaft'13 can bend so that the end 68 can move in any directiontransversely to the rotation axis of the thrust plate 4 and thattheinner member 63 of the universal j oint may'slide axially on the end 68of shaft 13. It will be seen,however, that rotation of the drive shaft 1is imparted directly to `the inner member 63 of the universal jointwithout any lost motion. The recess which accommodates the universaljoint is larger in diameter than any other available space between theconnecting rods or in the centre of the cylinder block'for the reasonthat the circle containing the centres of the connecting rod ball endsin the thrust plate is on a larger diameter than the circle of centresof the cylinders. This arrangement is essential in a pump or motor ofthe kind referred to to prevent the connecting rods, when in thepositions seen in the drawings, especially FIGURE 1, from contacting theopen ends of the cylinders.

Reference is now made to the example in FIGURES 3 and 4 in whichequivalent parts are given the same reference numerals as used inconnection with FIGURES 1 andA 2. The difference in construction fromFIGURE 2 lies in the provision of a secondary universal joint for 3 4connecting the inner member 63 of the universal joint 12 to the thrustplate 4. This allows free bodily universal movement. The form of FIGURES3 and 4 represents the most practical form of the invention. The bore 8extending from recess 10 is made comparatively shallow and within thisbore a transverse pin 69 is inserted through a transverse hole 71.Within the bore 8 a square-section block 72 fits on pin 69 to engageaccurately within a slot 73 which extends transverse to cylindrical plug74 which is a loose fit within bore 8. A short shaft extension 75extends from plug 74 and terminates as a splined end 68 engaging withinthe splined hole 67 in the centre member 63 of the universal joint. Thespindle or shaft extension 7S is locked in position by means of a nut 76screwthreaded on the end of the shaft 68 and a shoulder 77 which betweenthem grip on the inner member 63 of the universal joint. The pin 69 isnormally located in position by means of a sleeve 78 which surroundsshaft 1 and is located in position against a shoulder 79 by means of acirclip S1.

In operation,` it will be seen that the shaft extension 75 is capable oflimited bodily transverse angular movement relative to the axis of shaft1 and also capable of limited bodily longitudinal relative movement, butnot of relative rotational movement about the shaft axis which isprevented by the accurate engagement of the block 72 over the pin 69 andwithin the slot 73. Any small errors in the position of the universaljoint 12 so that its centre does not coincide with the intersection ofthe rotation axes of thrust plate and cylinder block are accommodated byvirtue of the limited transverse angular bodily movements andlongitudinal movements that shaft extension 75 may make relative to thethrust plate, whilst the fact that no relative rotation is allowed aboutthe drive shaft axis means that the cylinder block and thrust plate arerotationally interconnected without lost motion. The pin 69 and theblock 72 engaging in slot 73 form a secondary universal joint which needbe capable only of very small compensating movement, but this is abodily `movement as distinguished from the flexural movement in theforms of FIGURES 1 and 2. If it is desired to take the pump apart asduring servicing or repair, it may be necessary to part the thrust plateand the cylinder block. For this purpose, the circlip 81 and sleeve 78may be moved to allow pin 69 to be driven from the transverse hole 71 torelease plug 74 from recess 8 thereby releasing the vcylinder block fromthe thrust plate.

Referring now to FIGURE 5 of the drawings, the example shows amodification of the secondary universal joint of the type shown inFIGURES 3 and 4 in that the plug 74 is provided with a transverse slot73 which opens to the end of the plug. VThe purpose of this arrangementis to allow more easy parting of the cylinder block from the thrustAplate for service or repair. It will be seen that thereV is `no need toremove pin 69 since the open-ended slot 73 will slide olf the block 72.Other than this feature operation is as described for FIGURES 3 and 4'.

Referring now to FIGURE 6, the example shows a further `modification ofthe secondary universal joint shown in FIGURES 3 and 4 which permitsbodily movement. Within the recess 8 a plug 82 is positively xed bymeans of a pair of dowel pins extending through shaft 1 and within theplug a transverse slot 83 is formed which opens towards the universaljoint 12. This slot is closed at its ends by the walls of recess 8 toform a substantially rectangular section opening. The shaft extension 75extends into the slot and engages therein by means of a transverse pin84 extending through the shaft and a pair of Slide blocks 85 are squarein section to fit without lost motion across the slot. The outer end ofeach block is curved at 86 to engage the sides of recess 8 and to allowtransverse angular movement of shaft extension 75 relative to shaft 1 inthe plane of FIGURE 6. Pin 84 is tightly gripped in the end of shaftextension 75 but is free to move angulariy in the blocks 86.

Inoperation of the pump it will be seenV that slight inaccuracies inlocation of the universal joint 12 at the intersection of the rotationaxes of the cylinder block and thrust plate are accommodated by the factthat shaft extension 75 can movetransversely angularly to shaft 1 in anydirection by ,pivoting labout the axis of pin 84 and/ or pivoting abouta transverse axis tothe axis of pin 84 by virtue ofy opposite slidingmovements of blocks S in slot 83 and also by the fact that shaftextension 75 can move bodily in an axial direction of shaft 1 by similarsliding movements of the blocks 85. Relative rotational movement betweenshaft extension 75 and shaft 1 about their rotation axes is, however,positively prevented by the accurate engagement of blocks 85 .withinslot 83 .and the engagement of p in S4 within the blocks 85 thusensuring that there is no lost motion in the rotational drive betweenthrust plate and cylinder block. y

In all examples it will `be seen that the constant velocityuniversaljoint, of whatever specific type, is the drivinginterconnection between thrust plate and cylinder which transmits thedrive through the angle between thrust plate and cylinder block axesthus ensuring that there is accurate phase relation .between thrustplate and cylinder block at all rotational positions. block is drivensmoothly from the thrust plate without cyclic accelerations anddecelerations thereby avoiding high cyclic: torques on the constantvelocity universal joint. Further, provided that accurate phasealignment is v eifected between thrust plate and cylinder block duringmanufacture, as is intended by the structure of the Brown patent, the,connecting rods will liein planes substantially passing through therotation axis of the cylinder block'- at every angular position duringrotation thus ensuring that the connecting rods can exert no torque onthe cylinder block and on the constant velocity universal joint duringrotation. It is thereby ensured that the torque to be transmitted by theuniversal joint is substantially only that necessary to overcomefrictional resistance of the cylinder block. The constant velocityuniversal joint is located at a position where it can have the largestpossible diameter without interfering with the other working parts inparticular the connecting rods, and thus may have the greatest possibletorque capacity whilst at the same time only being subjected to a lowtorque. This ensures a very low rate of wear at the universal joint and,therefore, a trouble-free working life. The bodily movement of parts inthe secondary universal joint of FIGURES 3 to 6 inclusive allows entirefreedom for the small movements required, without restraint. Theflexural movement of shaft extension-13 combined with the bodily axialmovement of the splined connection at 67, 68 in FIGURE 2 achieves a likeresult.

We claim as our invention:

A hydraulic pump or motor of the class described comprising a rotarycylinder block formed with generally axially directed cylindersangularly spaced about its axis of rotation; a pistonreciprocative ineach cylinder; a drive shaft rotative at a constant rate; a rotarythrust plate driven by said drive shaft, and disposed in operation withThis ensures that the cylinder` itsaxis intersecting the axis of thecylinder block, as nearly as is. practicable, at an obtuse angle;vconnecting rods interconnecting the several pistons and the thrustplate, and arranged in planesradially of the cylinder blocks axis ofrotation; av two-part constantfvelocity type primary universal jointVlocated with its center substantially coincident with the intersectionof the two axes, and with its two parts lcoaxial respectively with thedrive shaft and with the cylinder block; a shaft extension secured to afirst part of the primary universal joint, that one of the cylinderblock or the drive shaft with which said iirst part is coaxial beingrecessed to receive said shaft extension loosely; the shaft extensionbeing slotted inwardly from its endthat' is distant from said rst partof the primary universal joint; a block closely received in and"slidable within said slot, and movable endwise into and from said slot;a pin anchoredA to said recessed member and directed transversely of theslot and through the block; said slotted shaft extension, block, and pinconstitutingl a secondary universal joint arranged` to permit relativebodily movement between' the parts so connected in the directiontransverseto their common rotative axis, and their relative bodilymovement inthe direction of such axis, to compensate for slightinaccuracy in location of the center of theprimary universal joint;.thesecondpart of .the pri References Cited inthe leof this patent UNITEDSTATES PATENTS 972,270 Smith Oct. 11, 1910 1,022,909 Whitney Apr. 9,1912 V1,346,253 Rayfield July 13, 1920 1,931,969 Thoma Oct. 24, 19332,072,090 Anderson Mar. 2, 1937 2,081,477 Egersdorfer May 25, 19372,133,176 Parent' Oct. 1l, 1938 2,146,133 Tweedale Feb. 7, 19392,153,093 Mageeet al. Apr. 4, 1939 2,178,331 Armstrong Oct. 31, 19392,231,117 ,Greiner Feb.` 11, 1941 2,319,100 Anderson May 11, 19432,565,208 Dietiker Aug. 21, 1951 2,623,604 Keese Dec. 30, 19522,649,741v j Henrischsen Aug. 2,5, 1953 2,670,614 Wildhaber Mar. 2, 19542,718,758 Minshall et al. Sept. 27, 1955 2,733,665 Klopp Feb. 7, 19562,834,297` Postelet. al May 13, 1958 2,900,921 Brown Aug. 25, 19592,908,151 Wahlmark Oct. 13, 1959 2,956,845 Wahlmark Oct. 18, 1960FOREIGN PATENTS D. 19,747 Germany May 9, 1956 1,034,980 Germany July 24,1958

